Porous ceramic molten metal composite solid oxide fuel cell anode

ABSTRACT

A fuel cell anode comprises a porous ceramic molten metal composite of a metal or metal alloy, for example, tin or a tin alloy, infused in a ceramic where the metal is liquid at the temperatures of an operational solid oxide fuel cell, exhibiting high oxygen ion mobility. The anode can be employed in a SOFC with a thin electrolyte that can be a ceramic of the same or similar composition to that infused with the liquid metal of the porous ceramic molten metal composite anode. The thicknesses of the electrolyte can be reduced to a minimum that allows greater efficiencies of the SOFC thereby constructed.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims the benefit of U.S. ProvisionalApplication Ser. No. 61/451,252, filed Mar. 10, 2011, which is herebyincorporated by reference herein in its entirety, including any figures,tables, or drawings.

The subject invention was made with government support under The UnitedStates Army, Contract No. 2008-ARM079-0001. The government has certainrights to this invention.

BACKGROUND OF THE INVENTION

Fuel cells combine oxygen and fuel to chemically generate electricitywithout combustion. Solid Oxide Fuel Cells (SOFCs) use ceramic materialsas an electrolyte, typically a solid yttria-stabilized zirconium oxide(YSZ), which is an excellent conductor of oxygen ions at hightemperatures. SOFC technology has the distinct advantage over competingfuel cell technologies (e.g. molten carbonate, polymer electrolyte,phosphoric acid and alkali) because of its ability to use fuels otherthan hydrogen and their relative insensitivity to CO, which act aspoisons to other fuel cell types, but is a fuel for these cells. Thegeneral design of a SOFC is two porous electrodes separated by a ceramicelectrolyte. The oxygen source, typically air, contacts the cathode, forexample strontium doped lanthanum manganese oxide (LSM), strontium dopedlanthanum cobalt iron oxide (LSCF), or other conventional cathodematerial, to form oxygen ions upon reduction by electrons at thecathode/electrolyte/oxygen triple phase boundary. The oxygen ionsdiffuse through the electrolyte material to the anode where the oxygenions encounter the fuel at the anode forming, water, carbon dioxide(with hydrocarbon fuels), heat, and electrons. The electrons transportfrom the anode through an external circuit to the cathode. Aparticularly useful anode for many cells is a liquid tin anode.

A Liquid Tin Anode Solid Oxide Fuel Cell (LTA-SOFC) is a fuel cell thatcombines the efficiency and reliability of conventional SOFCs whileexpanding the range of fuels that can be used, including gaseous,liquid, and solid fuels, and is particularly tolerant to impurities,such as sulfur. Another advantage is that coking is not a problem due tothe low catalytic activity of tin toward carbon depositions and becausethe tin is a low vapor pressure liquid at use temperatures, for example,above 232° C., such that a stable surface to promote excessive cokeformation is not available. Typically the tin is supported on the YSZelectrolyte, which is relatively thick.

Because of the thickness of the electrolyte, available LTA-SOFCs, whichare used at temperatures in excess of 1000° C., have power densitiesthat are significantly lower than other state of the art SOFCs,including those designed to function at lower temperatures, see forexample International Application Publication No. WO/2010/045329. Hence,a SOFC that combines a molten metal anode with a thin electrolyte tosignificantly lower the cells resistance is desirable.

BRIEF SUMMARY OF THE INVENTION

Embodiments of the invention are directed to a fuel cell anodecomprising a porous ceramic molten metal composite. Other embodiments ofthe invention are directed to a solid oxide fuel cell (SOFC) thatcomprises the anode comprising a porous ceramic molten metal composite.The porous ceramic molten metal composite comprises a metal or metalalloy that is infused into a porous ceramic and is liquid at atemperature below the working temperature of the SOFC. The metal ormetal alloy comprises tin, bismuth, indium, lead, antimony, copper,molybdenum, mercury, iridium, palladium, rhenium, platinum, silver,arsenic, rhodium, tellurium, selenium, osmium, gold, germanium,thallium, cadmium, gadolinium, chromium, nickel, iron, tungsten, cobalt,zinc, or vanadium and the porous ceramic comprises a doped CeO₂ orstabilized ZrO₂, such as Gd-doped CeO₂ (GDC), Y-doped CeO₂ (YDC),Sm-doped cerium oxide (SDC), Sm—Nd-doped cerium oxide, yttria-stabilizedzirconia (YSZ), Ca-stabilized zirconia, or Sc-stabilized zirconia.

The solid oxide fuel cell (SOFC) comprises a layer of the anodecomprising the porous ceramic molten metal composite, a cathode layercomprising a metal oxide or mixed metal oxide, and an electrolyte layercomprising an oxygen ion conductive ceramic. The cathode can comprise aperovskite-type oxide, such as LaMnO₃, La_(0.84)Sr0.₁₆MnO₃,La_(0.84)Ca_(0.16)MnO₃, La_(0.84)Ba_(0.16)MnO₃,La_(0.65)Sr_(0.35)Mn_(0.8)Co_(0.2)O₃,La_(0.79)Sr_(0.16)Mn_(0.85)CO_(0.15)O₃,La_(0.84)Sr_(0.16)Mn_(0.8)Ni_(0.2))₃,La_(0.84)Sr_(0.16)Mn_(0.8)Fe_(0.2)O₃,La_(0.84)Sr_(0.6)Mn_(0.8)Ce_(0.2)O₃,La_(0.84)Sr_(0.16)Mn_(0.8)Mg_(0.2)O₃,La_(0.84)Sr_(0.16)Mn_(0.8)Cr_(0.2)O₃,La_(0.6)Sr_(0.35)Mn_(0.8)Al_(0.2)O₃, La_(0.84)Scsub._(0.16)MnO₃,La_(0.84)Y_(0.16)MnO₃, La_(0.7)Sr_(0.3)CoO₃, LaCoO₃,La_(0.7)Sr_(0.3)FeO₃, La_(0.5)Sr_(0.5)CoO_(0.8)Fe_(0.2)O₃, or acomposite of a perovskite-type oxide and a solid electrolyte, forexample, LSCF-GDC or LSM-YSZ. The cathode layer can comprise a metaloxide or mixed metal oxide, for example, Bi₂Ru₂O₇ (BRO7),BRO7-(Er₂O₃)_(0.2)(Bi₂O₃)_(0.8) (ESB) composite,BRO-(Dw₂O₃)_(0.2)(Bi₂O₃)_(0.8)) (DSB) composite,BRO-(Y₂O₃)_(0.2)(Bi₂O₃)_(0.8)) (YSB) composite, orBRO-Bi_(2−(x+y))Dy_(x)W_(y)O₃ (DWSB) composite. The electrolyte layercan be GDC (Ce_(x)Gd_(1−x)O_(2−δ)), Y-doped CeO₂ (YDC)(Ce_(x)Y_(1−x)O_(2−δ)), Sm-doped cerium oxide (SDC)(Ce_(x)Sm_(1−x)O_(2−δ)), Sm—Nd-doped cerium oxide(Sm_(x)Nd_(y)Ce_(1−x−y)O_(2−δ)); yttria-stabilized zirconia (YSZ);Ca-stabilized zirconia; or Sc-stabilized zirconia. The electrolyte layercan be the same oxygen ion conductive ceramic included in the porousceramic molten metal composite of the anode layer. The electrolyte layercan be a bilayer electrolyte comprising a layer of the same oxygen ionconductive ceramic included in the anode layer and a layer of the metaloxide or mixed metal oxide of the cathode layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows an SEM image of a Sn/GDC composite anode, according to anembodiment of the invention, where Sn (dark grey) is intimately mixedwith GDC (light grey) and surrounded by continuous porosity (black) forgood fuel gas transport and oxidation, where each edge of the micrographis approximately 50 μm.

FIG. 2 plots the I-V characteristics of a SOFC at 600° C. for aSn—Ni/GDC anode, a GDC electrolyte, and an LSCF/GDC composite cathode,according to embodiments of the invention, where the data was collectedat 600° C. using flowing air at the cathode and wet hydrogen on theanode.

FIG. 3 plots the I-V characteristics of a SOFC at 600° C. for aSn—Ni/GDC composite anode, a GDC electrolyte, and an LSCF/GDC compositecathode, according to embodiments of the invention, where the data wascollected at 600° C. using vaporized flowing dodecane at the anode andair at the cathode.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the invention are directed to solid oxide fuel cells(SOFCs) that employ a porous ceramic molten metal composite anode with acathode, an electrolyte in contact with the anode and the cathode, andan electrical circuit connecting the anode and the cathode for use ofthe electrical power resulting from the chemical reaction generated bythe oxidation of the fuel. The oxidant, generally oxygen from the air isexposed to the cathode where it is reduced with the consumption ofelectrons to oxygen ions that transports through the electrolyte to theanode. Simultaneously, fuel is supplied to the anode where it reactswith the oxygen ion to form electrons and oxidation products, such aswater where the fuel is hydrogen, water and carbon dioxide when the fuelis a hydrocarbon, or carbon dioxide when the fuel is carbonaceous, withrelease of electrons as the fuel is oxidized. The electrons generated atthe anode are transmitted through the electrical circuit to the cathode.

Embodiments of the invention are directed to the porous ceramic moltenmetal composite anodes for use in SOFCs. The porous ceramic, for exampleGd-doped CeO₂ (GDC), not only supports the molten metal, for exampletin, but acts in a complementary fashion to the molten metal as itfacilitates oxygen diffusion into the anode from the electrolyte andwithin the anode to an extent that is not possible in the liquid metalalone due to the low solubility of oxygen ion in the metal, particularlythose of metal oxides that are formed where the fuel cell is operatedbelow the melting temperature of the metal oxide, when the metal isprone to formation of an insulating metal oxide at the electrolyteinterface.

A significant proportion of the fuel oxidation occurs at the triplephase boundary of the GDC/metal/fuel in the porous ceramic molten metalcomposite anode. The high electron conductivity of the molten metal andthe high oxygen ion conductivity of the porous ceramic combine in acomplementary fashion. As the anode is a composite that provides arelatively large triple phase boundary, it differs from a molten metalanode of a fuel cell that uses a porous ceramic only as the electrolyteor as a facilitating component that separates or controls the contactingof fuel to the separate molten metal anode. The composite structure isconstructed to optimize the area of the triple phase boundary of theoxygen conductive ceramic, the molten metal and the fuel. The porousceramic does not function as a barrier between the fuel and the anode,and allows the ceramic in conjunction with the liquid metal to displaygood electron transport as well as oxygen ion transport. The porousceramic used in the composite, according to embodiments of theinvention, can also provide a high electrical conductivity. Furthermore,the use of the porous ceramic molten metal composite anode allows use ofthin electrolytes in the solid oxide fuel cell (SOFC), which decreasesthe overall cell resistance and promotes superior cell performance. Inone embodiment of the invention, the electrolyte and the porous ceramicof the porous ceramic molten metal composite anode can be of the samematerial composition, which also reduces the cell's resistance.

In embodiments of the invention, the porous ceramic used in the porousceramic molten metal composite anode can be a doped ceria, (such asGd-doped CeO₂ (GDC) (Ce_(x)Gd _(1−x)O_(2−δ)) Y-doped CeO₂ (YDC)(Ce_(x)Y_(1−x)O_(2−δ)), Sm-doped cerium oxide (SDC)(Ce_(x)Sm_(1−x)O_(2−δ)), or Sm—Nd-doped cerium oxide(Sm_(x)Nd_(y)Ce_(1−x−y)O_(2−δ))) a metal-stabilized zirconia (such asyttria-stabilized zirconia (YSZ), Ca-stabilized zirconia, orSc-stabilized zirconia (SSZ)), or any other ceramic that can transportoxygen anions at high temperatures. Values for x or x+y for these porousceramics can range from less than 0.1 to about 0.5 and y can range from0.01 to 0.49 where optimal conductivities are observed. In an embodimentof the invention, the dopant level is 10-20 atom percent of the metal.

In embodiments of the invention, the molten metal of the porous ceramicmolten metal composite anodes can be a pure liquid or can have solid andliquid components as long as the overall properties of the metal areliquid-like at the working temperature of the SOFC. The anode can be apure metal or can comprise an alloy of two or more metals. In oneembodiment of the invention, the molten metal can display a standardreduction potential greater than −0.70 V versus the Standard HydrogenElectrode, as determined at room temperature. The molten metal anode cancomprise one or more transition metals, main group metals, alkalinemetals, alkaline earth metals, lanthanides, actinides, or anycombinations thereof. However, in many embodiments of the invention, themetal although liquid, possesses a low vapor pressure at the workingtemperature of the SOFC. Metals that can be included as the pure metalor a component of the alloy include tin, bismuth, indium, lead,antimony, copper, molybdenum, mercury, iridium, palladium, rhenium,platinum, silver, arsenic, rhodium, tellurium, selenium, osmium, gold,germanium, thallium, cadmium, gadolinium, chromium, nickel, iron,tungsten, cobalt, zinc, or vanadium. For example, Sn (M.P. 232° C.), Cd(M.P. 321° C.), Zn (M.P. 420° C.), Pb (M.P. 327° ° C.), Hg (M.P. −39°C.), Se (M.P. 221° C.), Tl (M.P. 304° C.), In (M.P. 156° C.), Bi (M.P.271° C.), Sb (M.P. 630° C.), and Te (M.P. 450° C.) can be used as thesingle component or the major components of an alloy matched to anoperating temperature above each metal's or alloy's melting point.Alloys include, but are not limited to, those with a primary metal thatis included at levels from 50 to 99% by weight. In embodiments of theinvention, the porous ceramic molten metal composite anode can be porousGDC with tin, or a liquid tin alloy, such as Sn—Ni, that can be usedwith hydrocarbon fuels at temperatures as low as 600° C.

The SOFC can be designed to operate where the metal of the porousceramic molten metal composite anode displays liquid or liquid-likeproperties at temperature of less than about 1,200° C., at a temperatureless than about 1,000° C., at a temperature less than about 900° C., ata temperature less than about 800° C., at a temperature less than about700° C., or at a temperature less than about 600° C. Those of ordinaryskill in the art can appreciate compositions for an anode or how toidentify compositions for an anode where temperatures that displayliquid or liquid-like behavior is achieved at a desired temperaturerange, for example from about 300° C. to about 1200° C., from about 500°C. to about 1100° C., from about 500° C. to about 1000° C., from about500° C. to about 800° C., from about 600° C. to about 1000° C., fromabout 600° C. to about 900° C., from about 600° C. to about 800° C.,from about 600° C. to about 700° C., from about 700° C. to about 1000°C., or from about 800° C. to about 1000° C. For example, Sn can be usedat temperatures above 300° C. whereas Sb requires temperatures above630° C. By addition of approximately 30 atom % Zn to Sb, the meltingtemperature is suppressed to ˜500° C. which allows operation at thistemperature. Near 30 atom % (+/−5) Zn, the alloy consists of a smallamount of solid phase within a large liquid phase at temperatures above˜500° C. and displays liquid like behavior, allowing its use in ananode, according to an embodiment of the invention. Higher levels of Znin the alloy with Sb result in a higher alloy melting temperature. Theporous ceramic molten metal composite anode resists coking when themetal, for example, tin, displays a low catalytic activity in additionto the presence of the liquid surface that does not stabilize carbondeposition. It is also advantageous when the metal is tolerant ofimpurities in the fuel. For example, liquid tin resists the blocking offuel oxidation reaction sites by sulfur and sulfur comprising compoundsand does not have promoted metal migration deficiencies that are commonwith typical non-liquid SOFC anodes.

The shape of the porous ceramic molten metal composite anode, theelectrolyte sharing a common interface, and the cathode can vary as isdesired to optimize any parameter for the SOFC including: overallvolume; surface area of any interface between the various functionallayers of the SOFC; effective surface area between the oxidizer andcathode; effective surface area between the fuel and anode; or any otherparameters that can facilitate or optimize heat exchange, fluid flows,or mixing, in a manner that can be appreciated by those of ordinaryskill in the art. For example, the SOFC can comprise a stack of flatplates or concentric cylinders.

The SOFCs, according to embodiments of the invention, can be constructedto employ fuels that are gases, such as hydrogen, methane, or naturalgas, liquids, such as hydrocarbons, or solids. The cells can be designedto introduce the fuel to the anode, and the oxidizer, for example, air,to the cathode in an efficient manner, as have been engineered for manystate of the art SOFCs with parallel plate, tubular, or other designs.

The cathode can be a perovskite-type oxide having a general structure ofABO₃, where “A” and “B” represent two cation sites in a cubic crystallattice. For example, the perovskite-type oxide can have the structureLa_(x)A_(a)B_(b)C_(c)O_(d) where A is an alkaline earth metal, B isselected from the group consisting of scandium, yttrium and a lanthanidemetal, C is selected from the group consisting of titanium, vanadium,chromium, iron, cobalt, nickel, copper, zinc, zirconium, hafnium,aluminum and antimony, x is from 0 to about 1.05, y is from 0 to about1, a is from 0 to about 0.5, b is from 0 to about 0.5, c is from 0 toabout 0.5, d is between about 1 and about 5, and at least one of x, y,a, b and c is greater than zero. Examples of perovskite-type oxidesinclude LaMnO₃, La_(0.84)Sr0.₁₆MnO₃, La_(0.84)Ca_(0.16)MnO₃,La_(0.84)Ba_(0.16)MnO₃, La_(0.65)Sr_(0.35)Mn_(0.8)Co_(0.2)O₃,La_(0.79)Sr_(0.16)Mn_(0.85)CO_(0.15)O₃,La_(0.84)Sr_(0.16)Mn_(0.8)Ni_(0.2)O₃,La_(0.84)Sr_(0.16)Mn_(0.8)Fe_(0.2)O₃,La_(0.84)Sr_(0.6)Mn_(0.8)Ce_(0.2)O₃,La_(0.84)Sr_(0.16)Mn_(0.8)Mg_(0.2)O₃,La_(0.84)Sr_(0.16)Mn_(0.8)Cr_(0.2)O₃,La_(0.6)Sr_(0.35)Mn_(0.8)Al_(0.2)O₃, La_(0.84)Scsub._(0.16)MnO₃,La_(0.84)Y_(0.16)MnO₃, La_(0.7)Sr_(0.3)CoO₃, LaCoO₃,La_(0.7)Sr_(0.3)FeO₃, La_(0.5)Sr_(0.5)CoO_(0.8)Fe_(0.2)O₃, or acomposite of a perovskite-type oxide and a solid electrolyte, forexample, LSCF-GDC or LSM-YSZ. The ceramic of the cathode may includeother elements, such as titanium, tin, indium, aluminum, zirconium,iron, cobalt, manganese, strontium, calcium, magnesium, barium, orberyllium. Other cathodes that can be used in the SOFCs with the porousceramic molten metal composite anodes include LaCoO₃, LaFeO₃, LaCrO₃,and a LaMnO₃-based perovskite oxide cathode, such asLa_(0.75)Sr_(0.25)CrO₃, (La_(0.6)Sr_(0.4))_(0.9)CrO₃,La_(0.6)Sr_(0.4)FeO₃, La_(0.6)Sr_(0.4)CoO₃ or Ln_(0.6)Sr_(0.4)CoO₃,where the lanthanide may be any one of La, Pr, Nd, Sm, or Gd. Thecathode of the SOFC can be a metal oxide or a mixed metal oxide,including Bi₂Ru₂O₇ (BRO7), BRO7-(Er₂O₃)_(0.2)(Bi₂O₃)_(0.8) (ESB)composite, BRO-(Dw₂O₃)_(0.2)(Bi₂O₃)_(0.8)) (DSB) composite,BRO-(Y₂O₃)_(0.2)(Bi₂O₃)_(0.8)) (YSB) composite, orBRO-Bi_(2−(x+y))Dy_(x)W_(y)O₃ (DWSB) composite. Alternatively, thecathode may include a metal. Examples of metals useful for the cathodesinclude platinum, palladium, gold, silver, rhodium, rhenium, iridium,osmium, and any combination thereof.

The electrolyte can be doped ceria (such as Gd-doped CeO₂ (GDC)(Ce_(x)Gd₁_31 xO_(2−δ)), Y-doped CeO₂ (YDC) (Ce_(x)Y_(1−x)O_(2−δ)),Sm-doped cerium oxide (SDC) (Ce_(x)Sm_(1−x)O_(2−δ)), or Sm—Nd-dopedcerium oxide (Sm_(x)Nd_(y)Ce_(1−x−y)O_(2−δ))), or metal-stabilizedzirconia (such as yttria-stabilized zirconia (YSZ), Ca-stabilizedzirconia, or Sc-stabilized zirconia (SSZ)). In some embodiments of theinvention, the electrolyte is of the same composition of the porousceramic include in the porous ceramic molten metal composite anode. Insome embodiments of the invention, the electrolyte can be a bilayerelectrolyte structured to complement both the anode and cathodestructures, for example a bilayer electrolyte can beCe_(x)Sm_(1−x)O_(2−δ)(SDC), Ce_(x)Gd_(1−x)O_(2−δ)(GDC), orSm_(x)Nd_(y)Ce_(1−x−y)O_(2−δ) with a bismuth oxide comprising layer ofBi_(1−x)Er_(x)O₃ (ESB), Bi_(2−x)Dw_(x)O₃ (DSB), Bi_(2−x)Y_(x)O₃ (YSB),or Bi_(2−(x+y))Dy_(x)W_(y)O₃ (DWSB), where the values of x or x+y canrange from less than 0.1 to about 0.5 and y can range from 0.01 to 0.49,where the cathode is a bismuth comprising cathode, such as BRO7, ESB,DSB, YSB, or DWSB.

Materials and Methods

A SOFC was prepared with a porous ceramic molten metal composite anode,where a Sn—Ni/GDC composite anode, as illustrated in FIG. 1, a GDCelectrolyte, and a LSCF/GDC composite cathode are combined. The SOFCcell was prepared by partially sintering a mixture of NiO/10GDC(Gd_(0.1)Ce_(0.9)O_(1.95)) into a pellet approximately 0.5 mm thick by2.5 cm in diameter. An aqueous suspension of 10GDC was applied on oneside of the pellet, forming a layer of GDC after drying. The pellet wassubsequently sintered to make a dense electrolyte of approximately 10 μmin thickness. A mixture of LSCF6428(La_(0.6)Sr_(0.4)Co_(0.2)Fe_(0.8)O_(3−δ))/10GDC powders in a paste formwith an organic solvent was applied to the 10GDC electrolyte layer,dried, and partially sintered to form a porous composite cathode ofapproximately 40 μm in thickness. Finally, a piece of tin metal wasfixed to the anode cell side using an organic adhesive. The SOFC wasused to generate power using hydrogen and dodecane as the fuel.

The SOFCs were tested under the following conditions. Air was applied tothe cathode side of the cell. The cell was heated to 600° C. with wet H₂on the anode side. During heating, NiO reduces to Ni and Sn melts toform an alloy with the Ni metal, resulting in the porous Sn—Ni/GDCanode. Currents were measured at a given voltage. After testing in wetH₂, vaporized dodecane was introduced to the anode side andcurrent-voltage measurements were performed.

As can be seen in FIG. 2, the SOFC using hydrogen with 3% water at thefuel at 600° C. where the open circuit potential (OCP) is 0.68 Vexhibits a maximum power density of 0.35 Wcm⁻² at 600° C. Usingvaporized dodecane at 600° C., as can be seen in FIG. 3, the SOFCdisplays an OCP of 0.86 V and a maximum power density of 0.25 Wcm⁻²,although some cell instability was apparent. The power densities arerepresentative of a good performing SOFC at 600° C. using wet H₂ asfuel, and this power density is also extended to operation using ahydrocarbon fuel such as dodecane, which is very high at 600° C.,representing a significant advance in the use of SOFCs for hydrocarbonfuel operation at an intermediate temperature, such as ˜600° C.

It should be understood that the examples and embodiments describedherein are for illustrative purposes only and that various modificationsor changes in light thereof will be suggested to persons skilled in theart and are to be included within the spirit and purview of thisapplication.

1. A fuel cell anode, comprising a porous ceramic molten metal compositewherein a metal or metal alloy that is liquid at the use temperature ofthe fuel cell is infused into a porous ceramic.
 2. The anode of claim 1,wherein the metal or metal alloy comprises tin, bismuth, indium, lead,antimony, copper, molybdenum, mercury, iridium, palladium, rhenium,platinum, silver, arsenic, rhodium, tellurium, selenium, osmium, gold,germanium, thallium, cadmium, gadolinium, chromium, nickel, iron,tungsten, cobalt, zinc, or vanadium.
 3. The anode of claim 1, whereinthe metal or metal alloy comprises tin.
 4. The anode of claim 1, whereinthe porous ceramic comprises a doped CeO₂ or doped ZrO₂.
 5. The anode ofclaim 1, wherein the porous ceramic comprises Gd-doped CeO₂ (GDC),Y-doped CeO₂ (YDC), Sm-doped cerium oxide (SDC), Sm—Nd-doped ceriumoxide, yttria-stabilized zirconia (YSZ), Ca-stabilized zirconia, orSc-stabilized zirconia (SSZ).
 6. The anode of claim , wherein the metalor metal alloy is liquid below 1,000° C.
 7. The anode of claim 1,wherein the metal or metal alloy is liquid below 650° C.
 8. A solidoxide fuel cell (SOFC), comprising: an anode layer comprising a porousceramic molten metal composite; a cathode layer comprising a metal oxideor mixed metal oxide; and an electrolyte layer comprising an oxygen ionconductive ceramic.
 9. The SOFC of claim 8, wherein the porous ceramicmolten metal composite comprises a metal or metal alloy comprising tin,bismuth, indium, lead, antimony, copper, molybdenum, mercury, iridium,palladium, rhenium, platinum, silver, arsenic, rhodium, tellurium,selenium, osmium, gold, germanium, thallium, cadmium, gadolinium,chromium, nickel, iron, tungsten, cobalt, zinc, or vanadium infused in aporous ceramic comprising Gd-doped CeO₂ (GDC), Y-doped CeO₂ (YDC),Sm-doped cerium oxide (SDC), Sm—Nd-doped cerium oxide, yttria-stabilizedzirconia (YSZ), Ca-stabilized zirconia, or Se-stabilized zirconia. 10.The SOFC of claim 9, wherein the porous ceramic molten metal compositecomprises a molten tin or tin alloy infused GDC.
 11. The SOFC of claim8, wherein the anode layer comprises a molten tin or tin alloy infusedGDC and the electrolyte layer comprises GDC.
 12. The SOFC of claim 8,wherein the metal oxide or mixed metal oxide comprises a perovskite-typeoxide.
 13. The SOFC of claim 12, wherein the perovskite-type oxidecomprises LaMnO₃, La_(0.84)Sr0.₁₆MnO₃, La_(0.84)Ca_(0.16)MnO₃,La_(0.84)Ba_(0.16)MnO₃, La_(0.65)Sr_(0.35)Mn_(0.8)Co_(0.2)O₃,La_(0.79)Sr_(0.16)Mn_(0.85)CO_(0.15)O₃,La_(0.84)Sr_(0.16)Mn_(0.8)Ni_(0.2)O₃,La_(0.84)Sr_(0.16)Mn_(0.8)Fe_(0.2)O₃,La_(0.84)Sr_(0.6)Mn_(0.8)Ce_(0.2)O₃,La_(0.84)Sr_(0.16)Mn_(0.8)Mg_(0.2)O₃,La_(0.84)Sr_(0.16)Mn_(0.8)Cr_(0.2)O₃,La_(0.6)Sr_(0.35)Mn_(0.8)Al_(0.2)O₃, La_(0.84)Scsub._(0.16)MnO₃,La_(0.84)Y_(0.16)MnO₃, La_(0.7)Sr_(0.3)CoO₃, LaCoO₃,La_(0.7)Sr_(0.3)FeO₃, or La_(0.5)Sr_(0.5)CoO_(0.8)Fe_(0.2)O₃.
 14. TheSOFC of claim 8, wherein the metal oxide or mixed metal oxide comprisesa composite of a perovskite-type oxide and a solid electrolyte.
 15. TheSOFC of claim 14, wherein the perovskite-type oxide and the solidelectrolyte metal oxide or mixed metal oxide comprises LSCF-GDC orLSM-YSZ.
 16. The SOFC of claim 8, wherein the metal oxide or mixed metaloxide comprises Bi₂Ru₂O₇ (BRO7), BRO7-(Er₂O₃)_(0.2)(Bi₂O₃)_(0.8) (ESB)composite, BRO-(Dw₂O₃)_(0.2)(Bi₂O₃)_(0.8)) (DSB) composite,BRO-(Y₂O₃)_(0.2)(Bi₂O₃)_(0.8)) (YSB) composite, orBRO-Bi_(2−(x+y))Dy_(x)W_(y)O₃ (DWSB) composite.
 17. The SOFC of claim 8,wherein the electrolyte layer comprises Gd-doped CeO₂ (GDC), Y-dopedCeO₂ (YDC), Sm-doped cerium oxide (SDC), or Sm—Nd-doped cerium oxide,yttria-stabilized zirconia (YSZ), Ca-stabilized zirconia, orSc-stabilized zirconia (SSZ).
 18. The SOFC of claim 8, wherein theelectrolyte layer comprises an oxygen ion conductive ceramic identicalto the ceramic of the porous ceramic molten metal composite of the anodelayer.
 19. The SOFC of claim 8, wherein the electrolyte layer comprisesa bilayer electrolyte comprising a layer of an oxygen ion conductiveceramic identical to the ceramic of the porous ceramic molten metalcomposite of the anode layer and a layer of the metal oxide or mixedmetal oxide of the cathode layer.